Irregular forest stands regeneration is considered using gap creation that provokes a light increase in the understorey. The light increase leads to the recruitment of new trees as well as the potential colonization by competitive herbaceous and shrubby species. This study focused on light interactions between Scots pine (Pinus sylvestris) seedlings and saplings and competitive vegetation made up of Calluna vulgaris, Molinia caerulea and Pteridium aquilinum growing in mixed sessile oak (Quercus petraea)-Scots pine stands in acidic temperate forests in France. The light was the key limiting factor controlling Scots pine seedling and sapling growth. Seedlings are able to tolerate a consequent shading, whereas sapling light requirement increases with their size. The growth of C. vulgaris, M. caerulea and P. aquilinum was measured according to light availability. For a given cover, P. aquilinum intercepted more light than M. caerulea and C. vulgaris. P. aquilinum involved a more pronounced decrease of pine seedling growth as this species was able to reach high cover even in very shaded conditions. For all the three species, processes like allelopathy, belowground competition or mechanical interference were assumed to also impede with pine seedling growth. All those results were integrated in a conceptual forest dynamics model named RReShar (Resource and regeneration Sharing).